I. Technical Field
The present invention relates to a cross groove constant velocity universal joint being a kind of a plunging type constant velocity universal joint, which is employed in a power transmission mechanism of an automobile or various industrial machines and is incorporated in a propeller shaft or a drive shaft used in, for example, a four-wheel drive (4WD) vehicle or a front-engine rear-drive (FR) vehicle.
II. Description of the Related Art
In some cases, a propeller shaft used in an automobile such as a 4WD vehicle or a FR vehicle includes a plunging type constant velocity universal joint called “cross groove joint” so as to cope with angular displacement resulted from change in relative position between a transmission and a differential.
FIGS. 7 to 10 illustrate an example of a cross groove constant velocity universal joint of a disk type. As illustrated in FIGS. 7 and 8, this constant velocity universal joint includes as main components an inner joint member 101, an outer joint member 102, balls 103, and a cage 104.
The inner joint member 101 has an outer peripheral surface in which a plurality of linear track grooves 106 are formed in the axial direction. Further, a shaft 107 is spline-fitted in a central hole 105 of the inner joint member 101, and torque can be transmitted between the shaft 107 and the inner joint member 101 owing to this spline-fitting. Note that the shaft 107 is prevented from being detached from the inner joint member 101 by a snap ring 108.
The outer joint member 102 is positioned along the outer periphery of the inner joint member 101, and has an inner peripheral surface in which linear track grooves 109 are formed in the axial direction by the same number as that of the track grooves 106 of the inner joint member 101. The cage 104 is arranged between the inner joint member 101 and the outer joint member 102, and the balls 103 are housed in pockets 110 of the cage 104.
The track grooves 106 of the inner joint member 101 and the track grooves 109 of the outer joint member 102 form, as illustrated in FIG. 9 (cage 104 is not shown), an angle inclined in the opposite direction with respect to an axial line L (track crossing angle α). The balls 103 are incorporated in crossing portions between the track grooves 106 (indicated by solid lines in FIG. 9) of the inner joint member 101 and the track grooves 109 (indicated by chain lines in FIG. 9) of the outer joint member 102, the track grooves 106 and the track grooves 109 being paired with each other. Further, the track grooves 106 adjacent to each other of the inner joint member 101 and the track grooves 109 adjacent to each other of the outer joint member 102 are arranged while being inclined in opposite directions to each other with respect to the axial line L by the track crossing angle α.
FIG. 10 is across sectional view illustrating the track grooves 106 of the inner joint member 101 and the track grooves 109 of the outer joint member 102. As illustrated in FIG. 10, the cross sectional shape of the track grooves 106, 109 is a shape of a gothic arch having the curvature radius larger than the radius of the balls 103 and formed by broaching or the like. The gothic arch shape allows the track grooves 106 of the inner joint member 101 and the track grooves 109 of the outer joint member 102 to contact each of the ball 103 at two points P, whereby angular contact having ball contact angles β is achieved. In this case, the ball contact angles β mean angles formed between ball contact centers P at which the ball 103 and the track grooves 106, 109 come into contact with each other and groove bottom centers Q of the track grooves 106, 109 with reference to a center Q of each of the balls 103.
On the other hand, to one axial end (left side in FIG. 7) of the outer joint member 102, an end cap 111 for preventing leakage of the lubricant filled inside the joint and invasion by foreign matters is fixed by bolting. Further, a sealing device is attached between the other axial end (right side in FIG. 7) of the outer joint member 102 and the shaft 107.
The sealing device includes a boot 112 and a boot adapter 113 made of metal. The boot 112 has a small end portion and a large end portion, and has a shape folded back at the middle portion in a V-shape. The boot adapter 113 is formed into a cylindrical shape, and has a flange, which is formed at one end thereof and fitted to the outer peripheral surface of the outer joint member 102. The boot adapter 113 is fixed to the outer joint member 102 together with the end cap 111 by bolting. The small end portion of the boot 112 is attached to the shaft 107 and clamped by a boot band 114. The large end portion of the boot 112 is retained by crimping the end portion of the boot adapter 113.
This constant velocity universal joint is disclosed in Universal Joint and Driveshaft Manual Section 3.2.12 “Cross Groove Universal Joint”. Universal Joint and Driveshaft Manual Section 3.2.12 “Cross Groove Universal Joint” describes a basic cross groove constant velocity universal joint including four or more (six in general) balls 103. Each of the track crossing angles α between the track grooves 106 of the inner joint member 101 and the track grooves 109 of the outer joint member 102 is designed to be such an angle that, when the constant velocity universal joint forms the maximum operating angle, the track grooves 106, 109 opposed to each other are not parallel to each other (13 to 19° in general). Further, the groove diameters of the track grooves 106, 109 having a gothic-arched cross section are set to be 1.01 to 1.04 times lager than the diameter of the balls, and the ball contact angles β are set to 30 to 45°.
Further, in the above-mentioned cross groove constant velocity universal joint, the track crossing angles α between the track grooves 106 of the inner joint member 101 and the track grooves 109 of the outer joint member 102 have relation to a sliding stroke of the joint. It is effective to reduce the track crossing angles α for increasing the stroke amount thereof.
However, when the track crossing angles α are reduced for increasing the sliding stroke of the joint, the maximum operating angle as the constant velocity universal joint becomes small. The maximum operating angle refers to an angle at which, when the joint is bent with not being rotated and then returned to the state before being bent, the maximum torque is applied. At worst, there occurs a phenomenon that the joint does not return to the former state with the angle being formed, and is hitched. The hitch during bending becomes a problem at the time of assembly of the constant velocity universal joint with respect to the automobile. That is, when assembling the constant velocity universal joint to the automobile, the operation for returning the joint to the former state after being bent once is necessary. Therefore, when the operating angle is small and the hitch occurs at the time of bending, efficiency in assembly operation of the constant velocity universal joint with respect to the automobile is low.
JP 2006-266423 A discloses means for preventing the maximum operating angle of the joint from being reduced and for increasing the sliding stroke by setting the track crossing angles α of the track grooves 106, 109 to 10 to 15° and by setting the number of balls 103 to be ten.
That is, in the cross groove constant velocity universal joint, when the balls 103 exist at a certain phase and the operating angle is increased, wedge angles formed at the crossing portions between the track grooves 106 of the inner joint member 101 and the track grooves 109 of the outer joint member 102 are reversed, whereby the force applied from the balls 103 to the cage 104 is imbalanced, and hence the cage 104 becomes unstable.
When the track crossing angles α of the track grooves 106, 109 are reduced, the above-mentioned phenomenon remarkably appears in the case of using six or less balls 103. However, in the case of using ten balls 103, even when the track crossing angles α are reduced, the cage 104 is stably driven up to a certain value. This is because driving force of the balls 103 in which the wedge angles are reversed is divided by the other balls 103 so that the driving of the cage 104 is stabilized.